The present invention relates to a coffee brewing apparatus and more specifically to an apparatus for the preparation of coffee based beverages such as espresso and capuccino.
A typical espresso apparatus includes components both for the brewing of espresso coffee and the heating/frothing of a volume of milk. In the brewing process, hot water is forced through the fine coffee powder at a pressure and temperature predetermined to provide the most suitable taste to the resulting coffee beverage. The process of forcing the water through the coffee powder pressed between perforated disks in the brew head of the espresso apparatus is called infusion. The temperature of the water is typically controlled by the amount of heat the water absorbs while flowing through a heat exchanger positioned within the boiler of the espresso apparatus. It is clearly desirable that the water under pressure be at a temperature which is most efficient for the infusion process.
It is difficult to ensure that the water reaching the brew head is at the precise desired temperature needed for quality infusion due to temperature drop after leaving the heat exchanger. The brew head acts as a heat sink causing much of the temperature drop. Typical prior art attempts to control the temperature of the brew head in an espresso apparatus use a pump to flow the water from the boiler through the brew head. However, such espresso devices suffer from slow response time and are cumbersome in design. Others attempt to raise the temperature of the water in the boiler to increase transfer of heat to the water flowing through the heat exchanger. This has not proven to be a satisfactory solution since the residual time of the water within the heat exchanger is not sufficient to effect the desired incremental change in heat transfer.
Espresso apparatus that also have components for heating/frothing milk generally employ a "steam wand" communicating with a steam zone in the same boiler that is immersed in a volume of milk in a container to raise the temperature of milk to acceptable levels and to provide the desired frothing. Cappucino beverages are ordinarily comprised of one third espresso, one third hot milk, and one third froth. When steam is used for the heating and/or frothing, there is a delay in recovery of the steam zone before the same cycle can again be initiated. The amount of heat input to a boiler heated by electricity is limited by the voltage and current rating of the electrical supply outlet into which the apparatus is plugged. Where 240 volt outlets are available, the delay generally is not a problem since the recovery time of the apparatus in producing steam is acceptable. However, it becomes a serious problem when locally available electric power comes from 120 volt circuits. Sacrifices must be made which typically means that insufficient steam may be available for the proper heating and frothing of milk. Discerning consumers of coffee based beverages, accustomed to the greater power available for such espresso devices where 240 volt outlets are available for brewing and frothing, can readily detect the difference when the milk is under heated or frothed.